Motor vibration suppression mounting



Aug. 30, 1966 P. B. SHAFFER 3,270,221

MOTOR VIBRATION SUPPRESSION MOUNTING Original Filed Dec. 11, 1962 :5Sheets-Sheet l ELELL [UIUUUUD u l N VENTOR.

Raul 5. S/Yaff'en fizi'tozweg.

Aug. 30, 1966 P. B. SHAFFER MOTOR VIBRATION SUPPRESSION MOUNTINGOriginal Filed Dec. 11, 1962 3 Sheets-Sheet 115m 100mm Aug. 30, 1966 F'.B. SHAFFER 3,

MOTOR VIBRATION SUPPRESSION MOUNTING Original Filed Dec. 11, 1962 (5Sheets-Sheet 3 ELLE-E FOPC/NG FREQUENCY i uA/onmpa-p NHTUIPAZ fa gmwcyINVENTOR.

United States Patent 3 MOTOR VIBRATION The present application is acontinuation of my oopending application Serial No. 243,902, nowabandoned, filed December 11, 196 2. This invention relates to improvedmotor mounting arrangements and more particularly to such motor mountingarrangements wherein the transmission of axial vibrations to the supportor apparatus on which the motor is mounted is minimized.

Axial vibrations caused by operating rotating machines, such as motors,from a cyclically varying power supply, such as a 60 cycle alternatingpower source, may cause objectionable noise and may unduly excite thesupport members on which the rotating machine is mounted unless someprovision is made to isolate the axial vibrations. The problem ofeffectively isolating the vibration of the rotating machine becomescritical in applications where the machine is suspended in a verticalposition from a main support and particularly where a frictional type ofdriving connection, such as a belt and pulley, is employed. In suchapplications, the support in which the rotating machine is mounted by besubjected to axial, torsional and radial forces resulting from theweight and vibratory motion of the rotating machine.

Where a mot-or is mounted or supported by a housing or frame of theapparatus in which the motor is employed, the virbatory motion of themotor is transmitted to the frame or housing. Thus, the panels or otherparts which comprise the frame or housing of the apparatus may vibratewith the motor. Conventionally, resilient cushion rings have beenemployed to minimize the effect of these vibrations, especially in smalldynamoelectric machines, such as fractional horsepower motors. Suchconventional resilient mountings utilize an annular cushion ring ofresilient material fitted generally at each end of the motor and a basemember arranged to support the resilient cushion ring. This type ofresilient mounting construction has not proven to be satisfactory inmany applications. For example, where the motor must be suspended andsupported at only one end, such a resilient mounting arrangement cannot,of course, be used with conventional base designs. It will beappreciated, also, that the cushion ring type of mounting arrangement isnot adaptable for use in many motor frame configurations which do notreadily permit the use of cushion rings at the ends of the motor.Moreover, the cushion ring type of mounting arrangement is relativelyexpensive to manufacture.

It is, therefore, desirable to provide a mounting arrangement for adynamoelectric machine, such as a motor, wherein vibrations produced bythe motor are effectively isolated from the support members at theapparatus on which the motor is mounted. It is also desirable that themounting arrangement be readily adaptable to existing motorinstallations so that vibration problems when encountered can becorrected without requiring any extensive modifications of the motor orthe support members. These advantages should, of course, be achievedeconomically and with an efl icient utilization of materials and labor.

Accordingly, it is an object of the invention to provide an improvedmounting arrangement for a dynamoelectric machine, such as a motor,whereby vibrations produced by the motor during operation areeffectively isolated from the apparatus on 'which the motor is mounted.

A more specific object of the invention is to provide an improvedmounting arrangement for a motor which is readily adapted for convertingmotorts installed in an apparatus without any vibration isolatingmounting.

It is a further object of the invention to provide an improved motormounting arrangement that can be economically manufactured and that isrelatively inexpensive to produce and to install.

Another object of the invention is to provide an improved motor mountingarrangement for isolating motor vibrations that is particularlyadaptable to applications in which the motor is supported at one end inan essentially vertical position.

According to one form of my invention, I have provided an improvedarrangement for mounting an electric motor on a support. In the mountingarrangement, a vibration isolating base member is disposed at one end ofthe motor. A plurality of attaching members are provided for securingthe vibration isolating base member to the support. The attachingmembers divide the vibration isolating member into beam portions whichare fixedly supported at each end by the attaching members and provide adeflectable support for the motor. The motor is secured to the vibrationisolating member at an intermediate position on each of the beamportions. The beam portions are proportioned so that the ratio of theforcing frequency of the motor to the natural frequency of the vibrationisolating member is held within predetermined limits to control thetransmissibility of the vibrations produced by the motor to the supportor apparatus and which the motor is mounted below a preselected value aswill be explained in more detail hereinafter, the proportions of thebeam portions for a given motor application may be determined inaccordance with the expression:

Pl 192EI where d is the deflection of the individual beam portions ininches; P is the concentrated load of the motor being supported at eachbeam portion in inches; 1 is the length of the beam portions in inches;192 is a numerical unit conversion constant; E is the modulus ofelasticity in pounds per square inch for the beam portions; and I is themoment of inertia in inches to the fourth power.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. My invention, itself, both as to its organization andmethod of operation, together with further objects and advantagesthereof, may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawings inwhich:

FIGURE 1 is a fragmentary view of an end of a motor incoporating theimproved mounting arrangement of the invention;

FIGURE 2 is a plan view of the vibration isolating base member used inthe preferred embodiment of the invention illustrated in FIGURE 1;

FIGURE 3 is an end view of the vibrating isolating base member shown inFIGURE 2;

FIGURE 4 is a fragmentary view of the right end of the vibrationabsorbing base member as shown in FIG- URE 3, the view being enlarged toshow the details;

FIGURE 5 illustrates an electric motor being suspended from a supportmember by the improved mounting construction of one form of the presentinvention; and

FIGURE 6 shows a plot of the transmissibility ratio T against the ratiof/f the ratio of the forcing frequency to the natural frequency forvarious values of the damping constant ratio of C/C in a single degreeof freedom system.

Referring now to the drawings, there is shown in FIG- URE 1 an electricmotor of the type used in a domestic washing machine or other appliancesand in FIG- URES 2, 3, and 4, a vibration isolating member 11 arrangedin accordance with the invention. The electric motor 10 as shown iscomprised of the vibration isolating base member 11, a main frame member12, an end shield assembly 13, and a rotatable rotor shaft 14 extendingupwardly through the end shield member 13.

In order to attach the motor 10 to the driven apparatus (not shown), thevibration isolating base member 11 is provided with four equispacedstuds 16, 17, 18 and 19. Also, it will be noted that the vibrationisolating base member 11 is provided with four equispaced clearanceholes 20, 21, 22, 23, and as shown in FIG- URE 2, are adapted forreceiving the through bolts 24, 25, 26 and a through bolt which is notseen in the view shown.. The through bolts hold the end shield assembly13 in assembled relation with the main frame member 17 of the motor 10.It will be noted that the spacing between the studs 16, 17, 18, and 19is equal to the spacing of the through bolts. This arrangement resultsin the advantage that in installations where a motor was attached to theapparatus by means of the through bolts without a vibration isolatingmeans, the vibration isolating member of the invention can be readilyinstalled. It Will be appreciated that in such existing installations avibration problem can be solved with-out need for modifying the motor10. Further, it is not required to change the support on which the motor10 is mounted since the clearance holes on the support which are adaptedto receive through bolts can be also used to receive the mounting studsof the vibration isolating member 11. Thus, an important advantage ofthe arrangement used in the illustrated embodiment of the invention isthat noise or vibrations caused by a motor installed in an appliance canbe readily minimized without any extensive modifications to either themotor or the apparatus. In order to correct the vibration condition, itis only required to disconnect the motor, install the vibrationisolating base member 11 as shown in FIGURE 1 and then to reassemble themotor on the apparatus.

Referring now more particularly to the views of the vibration isolatingmember 11, as shown in FIGURES 2, 3, and 4 of the drawings, it will beseen that the vibration isolating base member 11 is comprised of a stackof three annular-shaped plates or laminations 30, 31, 32. In theillustrated embodiment of the invention, uncut stator laminations wereused for the plates. The annular plates 30, 31, 32 were cementedtogether by a resilient caulking cement 33, which did not harden butremained relatively plastic or viscous so as to improve the dampingcharacteristics of the vibration isolating base member 11. The studs 16,17, 18 and 19 were silver soldered to the annular plates. As will behereinafter more fully explained, the studs 16, 17, 18 and 19 divide thebase member 11 into four beam portions and serve as fixed supports forthe beam portions. The number of annular plates 30, 31, 32 was used tocontrol the natural frequency of the vibration isolating base member 11.It will be appreciated that other factors, such as the number of beamportions can be varied to provide the desired natural frequency.Further, resilient annular shaped members may be interposed between theannular plates 30, 31, 32 to improve the damping characteristics of thevibration isolating base member 11, if necessary.

In FIGURE 5, I have illustrated a motor 40 that is vertically suspendedon a support member 41 by a mounting arrangement in accordance with theinvention. In this exemplification of the invention, a vibrationisolating base member 42 comprised of a single annular plate is utilizedto effectively minimize the motor vibrations transmitted to the supportmember 41.

The motor 40 is substantially enclosed in a housing which includes framemember 43 and a pair of end shield members 44, 45, the end shieldmembers 44, 45 being secured by four throughbolts only three of which46, 46a, 47 are seen in FIGURE 5. The through bolts hold the vibrationisolating base member 42 in assembled relation with the motor 40. Fourstuds, only two of which 48, 49 are seen in the view shown, are used tosecure the vibration isolating base member 42 to the frame member 41. ashaft 50 is rotatably mounted in bearing assemblies supported in the endshield members 44, 45

In carrying out the present invention in practice, the vibrationisolating member is proportioned so that the ratio of the forcingfrequency f to the natural frequency f is held within predeterminedlimits so that the transmissibility of vibrations produced by the motorare effectively minimized. For a vibration isolating base member 11having four equispaced studs 16, 17, 18 and 19, the portions of themember 11 between the studs may be considered as simple fixed beams witha concentrated load being applied at the center of the beam. The naturalfrequency f,, of the vibration isolating member 11 is dependent upon adeflection of these individual beams and is equal to 3.13/ d, where f isthe natural frequency of the system in cycles per second, and d is thedeflection of the vibration isolating member in inches.

The motor 11 used in the exemplification of the invention was a fourpole motor operating at 1,725 revolutions per minute and was energizedfrom a 60 cycle power supply. The maximum forcing frequency occurred atcycles per second and a second forcing frequency occurred once perrevolution or at a frequency of 28.75 cycles per second. It will beappreciated that if the vibration isolating base member 11 had a naturalfrequency near any one of these two forcing frequencies, in the absenceof a very high damping factor, these forcing frequencies would bemultiplied. Accordingly, a suitable value for the natural frequency ofthe vibration isolating member 11 was selected whereby thetransmissibility of the motor vibrations was effectively minimized aswill now be more fully explained.

For the purpose of determining the transmissibility of the motorvibrations to a support, the motor 10 and the vibration isolating basemember 11 were assumed to be a single degree of freedom system. InFIGURE 6, I have illustrated a series of curves representing a plot oftransmissibility T versus the ratio f/j, for various values of thedamping ratio C/C where C is the damping factor of the vibrationisolating member 11 and C is the critical damping factor. For thevibration isolating member 11 employing three stator laminations bondedwith a relatively soft or pliable bonding cement, it was found that thedamping ratio was approximately 0.2. The transmissibility T is the ratioof the displacement amplitude of the motor 40 to that of the base member11 and is a function of the frequency ratio f/f and the damping ratioC/C as is set forth in FIGURE 6.

If we take 40 cycles per second as a predetermined value for theundamped natural frequency of the base member 11, it will be seen thatthe curve corresponding to a damping ratio of 0.2 for a frequency ratioof 120/40 or 3, the transmissibility T is approximately 0.20. For the28.75 cycle excitation, the frequency ratio f/y is approximately 0.72,and from the curve in FIGURE 6 corresponding to a damping ratio of 0.2,we obtain a value of 1.8 for the transmissibility T. Thus, the twovalues for the transmissibility T appear to be satisfactory.

The vibration isolating member 11 used in the exemplification of theinvention was proportioned to provide a natural frequency of 40 cyclesper second by varying its thickness. The deflection due to gravity of n,b portion of the member 11 in inches corresponding to a naturalfrequency of 40 cycles Per second is equal to the square of 3.13/40 or.00614.

If we assume that the beam portion of th vib i lsolatlng member 11 is aSimple fixed beam with a concentrated load at the center, the thicknessof a singl lamination of member 11 can be determined from the followingexpression for the deflection d of a fixed beam:

where P is A of the weight of the motor divided by the number of platesor 1 pound; l is the length of the beam of 4 inches; E is the modulus ofelasticity in pounds per square inch which for steel is 30x10 and I isthe moment of inertia or /2 the width (1.4 inches) of the beam portiontimes W, h being the thickness in inches.

For the specific illustrative example in the value of thickness h wasfound to be approximately .0249 inch. The vibration isolating member 11was constructed of three laminations having a thickness of .025 inch toprovide a member having a natural frequency of 40 cycles per second.

From the foregoing description of the preferred embodiment and of thespecific example presented by way of a particular exemplificationthereof, it will be apparent that the transmissibility of the motorvibrations to the support can be controlled by proportioning the beamportions to provide a vibration isolating member having the desirednatural frequency. It will be apparent that other dimensions of the beamportion may be varied. For example, the number 'of the beam portions canbe varied so as to change the effective beam length. Further, it will beappreciated that although a vibration isolating base member having anannular shape was employed, other configurations can be used in carryingout the present invention.

It should be apparent to those skilled in the art, that while I haveshown what presently is considered to be a preferred embodiment of myinvention that changes and modifications can be made without actuallydeparting from the true spirit and scope of the invention. It is,therefore, intended to cover in the appended claims all such equivalentvariations as fall within the invention.

What I claim as new and desired to secure by Letters Patent of theUnited States is:

1. In an arrangement for mounting an electric motor on an apparatus, anelectric motor, a vibration isolating base member, and motor vibrationtransmissibility controlling means for holding a ratio of forcingfrequency f of the motor to natural frequency f of the vibrationisolating member within predetermined limits to control transmissibilityof vibrations produced by the motor to the apparatus below a preselectedvalue, said transmissi-bility controlling means comprising anattachingmeans adapted for securing said vibration isolating base member to theapparatus, said attaching means dividing said vibration isolating basemember into a preselected plurality of deflectable beam portion means,said attaching means being adapted for providing a fixed support at eachend for said deflectable beam portion means, securing means forattaching said motor at an intermediate position on each of saiddeflectable beam portion means to provide a deflectable support for saidmotor, said deflectable beam portion means having predeterminedproportions for holding the ratio of the forcing frequency of the motorto the natural frequency of the vibration isolating member within saidpredetermined limits, said predetermined proportions of the beam portionmeans being determined in accordance with the expression P13 192EI whered is the deflection of the beam portion means in inches,

P is the concentrated load of the motor being supported in pounds,

I is the length of the beam portion means in inches,

192 is a numerical constant,

E is the modulus of elasticity in pounds per square inch for the beamportion means, and

I is the moment of inertia in inches to the fourth power,

whereby the transmissibility of the vibrations produced by the motor tothe apparatus is effectively controlled.

2. In a motor mounting arrangement for mounting an electric motor on asupport, a vibration isolating base member formed of at least onegenerally annular-shaped plate means, an electric motor having a housingsupporting the stator and rotor for relative rotation, and motorvibration transmissibility controlling means for holding the ratio offorcing frequency f of the motor to natural frequency f of the vibrationisolating member within predetermined :limits to controltransmissibility of vibrations produced by the motor to the supportbelow a preselected value, said vibration transmissibility controllingmeans comprising attaching means for fixedly attaching said vibrationisolating base member to a support, said attaching means dividing saidmember into deflectable beam portion means adapted to be supported atthe ends thereof, securing means fixedly securing said motor at aposition intermediate of the ends of each of said deflectable beamportion means, said deflectable beam portion means defining adeflectable support for said motor and having predetermined proportionsfor holding the ratio of the forcing frequency of the motor to thenatural frequency of the vibrations isolating member within saidpredetermined limits, said predetermined proportions of the beam portionmeans being determined in accordance with the expression where d is thedeflection of the beam portion means in inches;

P is the concentrated load of the motor being supported in pounds,

I is the length of the beam portion means in inches,

192 is a numerical constant,

E is the modulus of elasticity in pounds per square inch for the beamportion means, and

I is the moment of inertia in inches to the fourth power.

whereby the transmissibility of the motor vibrations to the support forthe motor is effectively controlled.

3. In an arrangement for mounting a motor on a support, an electricmotor having a housing substantially enclosing the stator and rotor, avibration isolating base member disposed at one end of said motor, saidvibration isolating base member being comprised of a stack of flatdeflectable plates, a resilient means interposed between said plates toprovide the desired damping characteristics in said vibration isolatingbase member, a plurality of attaching members adapted for attaching thevibration isolating base member to a support, said attaching membersdividing the vibration isolating base member into a plurality of beamportions to provide a fixed support for said beam portions at the endsthereof, means for attaching said vibration isolating base member infixed relation with the housing of the motor at intermediate pointsbetween the ends of each of said beam portions, said beam portionsproviding a deflectable support for said motor and being proportioned sothat the ratio of the forcing frequency of the motor to the naturalfrequency of the vibration isolating base member is maintained withingpredetermined limits to minimize the transmissibility of vibrations tothe support for the motor.

4. In an arrangement for mounting an electric motor in a support withthe rotatable shaft of the motor disposed in a vertical position, avibration isolating base member comprised of a stack of at least twodeflectable laminations having resilient means interposed therebetween,a plurality of generally equispaced attaching members fixedly attachedto said vibration isolating member, said attaching members being adaptedfor securing said vibration isolating base member into a plurality ofdeflectable beam portions, and means attaching said motor 7 to saidvibration isolation member at an intermediate location on each of saiddeflectable beam portions, said deflectable beam portions, providing adeflectable support for said motor to minimize the transmission of themotor vibrations to the support.

'5. In a motor mounting arrangement for supporting an electric motor, avibration isolating base member disposed at one end of said motor, saidvibration isolating base member being comprised of a stack ofannularshaped plates, said plates being laminated with a resilientcement, a plurality of axially extending studs mounted in equispacedlocations on said vibration isolating base a member, said studs beingadapted for securing said vibration isolating base member to a supportand dividing said vibration isolating base member into a plurality ofbeam portions, said stubs being adapted to provide a fixed support atthe ends thereof, and, means attaching each of said beam portions at anintermediate point thereon in force transmitting relation with saidmotor, said vibration isolating member being proportioned so that theratio of the forcing frequency of the motor vibrations to the naturalfrequency of the vibration isolating base member is maintained withinpredetermined limits in order to minimize the transmission of the motorvibrations to the support.

6. In a motor mounting arrangement for suspending an electric motor in avertical position from a support; an electric motor having an upper endshield member assembled to a main frame member by means of a pluralityof equispaced through-bolts; vibration isolating base means comprised ofat least two relatively thin plates having resilient means interposedtherebetween; said vibration isolating base means being fixedly attachedto said upper end shield member and in spaced relationship therewith bysaid through-bolts; and a plurality of equispaced attaching membersfixedly attached to said vibration isolating base means at intermediatelocations between said through-bolts and dividing said vibrationisolating base means into a plurality of deflectable beam portions; saidvibration isolating base means having pre determined proportions forholding the ratio of the forc ing frequency of the motor vibrations tothe natural frequency of the vibration isolating mem'ber means withinpredetermined limits to minimize the transmission of the motorvibrations to the support.

References Cited by the Examiner UNITED STATES PATENTS 1/1940 Castricone310-51 9/1949 Bonthron 31051 ORIS L. RADER, MILTON O. HIRSHFIELD,

' Examiners.

I. W. GIBBS, Assistant Examiner,

1. IN AN ARRANGEMENT FOR MOUNTING AN ELECTRIC MOTOR ON AN APPARATUS, ANELECTRIC MOTOR, A VIBRATION ISOLATING BASE MEMBER, AND MOTOR VIBRATIONTRANSMISSIBILITY CONTROLLING MEANS FOR HOLDING A RATIO OF FORCINGFREQUENCY F OF THE MOTOR TO NATURAL FREQUENCY FN OF THE VIBRATIONISOLATING MEMBER WITHIN PREDETERMINED LIMITS TO CONTROL TRANSMISSIBILITYOF VIBRATIONS PRODUCED BY THE MOTOR TO THE APPARATUS BELOW A PRESELECTEDVALUE, SAID TRANSMISSIBILITY CONTROLLING MEANS COMPRISING AN ATTACHINGMEANS ADAPTED FOR SECURING SAID VIBRATION ISOLATING BASE MEMBER TO THEAPPARATUS, SAID ATTACHING MEANS DIVIDING SAID VIBRATION ISOLATING BASEMEMBER INTO A PRESELECTED PLURALITY OF DEFLECTABLE BEAM PORTION MEANS,SAID ATTACHING MEANS BEING ADAPTED FOR PROVIDING A FIXED SUPPORT AT EACHEND FOR SAID DEFLECTABLE BEAM PORTION MEANS, SECURING MEANS FORATTACHING SAID MOTOR AT AN INTERMEDIATE POSITION ON EACH OF SAIDDEFLECTABLE BEAM PORTION MEANS TO PROVIDE A DEFLECTABLE SUPPORT FOR SAIDMOTOR, SAID DEFLECTABLE BEAM PORTION MEANS HAVING PREDETERMINEDPROPORTIONS FOR HOLDING THE RATIO OF THE FORCING FREQUENCY OF THE